Variability in high-salinity shelf water production in the Terra Nova Bay polynya, Antarctica

Seung-Tae Yoon,Jiyeon Lee,Craig Stevens,Gwang Il Jang,Won Sang Lee,Sukyoung Yun,Sunghyun Nam,Stefan Jendersie,Chung Yeon Hwang

doi:10.5194/os-16-373-2020

Abstract

Abstract. Terra Nova Bay in Antarctica is a formation region for high-salinity shelf water (HSSW), which is a major source of Antarctic Bottom Water. Here, we analyze spatiotemporal salinity variability in Terra Nova Bay with implications for the local HSSW production. The salinity variations in the Drygalski Basin and eastern Terra Nova Bay near Crary Bank in the Ross Sea were investigated by analyzing hydrographic data from instrumented moorings, vessel-based profiles, and available wind and sea-ice products. Near-bed salinity in the eastern Terra Nova Bay (∼660 m) and Drygalski Basin (∼1200 m) increases each year beginning in September. Significant salinity increases (>0.04) were observed in 2016 and 2017, which is likely related to active HSSW formation. According to velocity data at identical depths, the salinity increase from September was primarily due to advection of the HSSW originating from the coastal region of the Nansen Ice Shelf. In addition, we show that HSSW can also be formed locally in the upper water column (<300 m) of the eastern Terra Nova Bay through convection supplied by brine from the surface, which is related to polynya development via winds and ice freezing. While the general consensus is that the salinity of the HSSW was decreasing from 1995 to the late 2000s in the region, the salinity has been increasing since 2016. In 2018, it returned to values comparable to those in the early 2000s.

Highlights

The strength of the global meridional overturning circulation is closely associated with the production of Antarctic Bottom Water (AABW) (Jacobs, 2004; Johnson, 2008; Orsi et al, 1999, 2001), and approximately 25 % of the AABW is produced in the Ross Sea (Orsi et al, 2002)
Model results suggest that the modified Circumpolar Deep Water (CDW) (MCDW) is advected as far south as Crary Bank east of Terra Nova Bay (TNB) (Dinniman et al, 2003; Jendersie et al, 2018), this has yet to be confirmed by observation
Salinity observed at the deepest sensor (660 m) at the DITN mooring located in the eastern TNB (Fig. 1) exhibited interannual variations during 2015–2017 (Fig. 4a) and increased from 34.80 to 34.85

Summary

Introduction

The strength of the global meridional overturning circulation is closely associated with the production of Antarctic Bottom Water (AABW) (Jacobs, 2004; Johnson, 2008; Orsi et al, 1999, 2001), and approximately 25 % of the AABW is produced in the Ross Sea (Orsi et al, 2002). Model results suggest that the modified CDW (MCDW) is advected as far south as Crary Bank east of Terra Nova Bay (TNB) (Dinniman et al, 2003; Jendersie et al, 2018), this has yet to be confirmed by observation. AABW is formed by the mixing of HSSW and CDW or MCDW (Budillon and Spezie, 2000; Budillon et al, 2011; Cincinelli et al, 2008; Gordon et al, 2009). Of the HSSW in the Ross Sea, 33 % is produced in the Terra Nova Bay polynya (TNBP) (Fusco et al, 2009; Rusciano et al, 2013; Jendersie et al, 2018). The Drygalski Ice Tongue (DIT), which forms the southern boundary

Results

Discussion

Conclusion